Born in Yokosuka, Japan on February 9, 1978, to Filipino parents – hence his nickname, ‘The Filipino Wrecking Machine’ – Muñoz moved to Vallejo, California as an infant. An individual gold medallist in the 197lb weight class at the National Collegiate Athletic Association (NCAA) Division I Wrestling Championships in Iowa City in 2001, while a senior at Oklahoma State University, Muñoz made his MMA debut in the Palace Fighting Championship (PFC) at the Tachi Palace Hotel & Casino in Lemoore, California on July 19, 2007. On that occasion, he beat Austin Achorn by technical knockout after 1:25 of the opening round.
The following April, Muñoz left his position as assistant coach at the University of California, Davis to pursue a professional MMA career. He made his World Extreme Cagefighting (WEC) debut on June 1, 2008 at the Arco Arena in Sacramento, California. On the main card at ‘WEC 34: Faber vs. Pulver’, he competed in the light heavyweight division, defeating Chuck ‘The Reverend’ Grigsby by knockout after 4:15 of the first round. Another first-round victory, by technical knockout, over Ricardo Barros on the preliminary card of ‘WEC 37: Torres vs. Tapia’, at the Hard Rock Hotel & Casino in Paradise, Nevada on December 3, 2008, took his MMA record to 5-0.
Following the elimination of the light heavyweight and middleweight weight classes from WEC, Muñoz was one of a handful of fighters selected to make the transition to the Ultimate Fighting Championship (UFC) which, like WEC, was owned and produced by parent company Zuffa, LLC. He made his UFC debut on the main, pay-per-view (PPV) card at ‘UFC 96: Jackson vs. Jardine’ at the Nationwide Arena in Columbus, Ohio on March 7, 2009. However, the light heavyweight contest against Matt ‘The Hammer’ Hamill ended in the first defeat of his career when he was knocked out by a head kick after 3:53 of the first round.